1. Field of the Invention
The present invention relates to an information processing system, information processing apparatus, information processing method, and recording medium.
2. Description of the Related Art
Conventionally, a technique called DRM (Digital Rights Management) is used to manage the copyrights of contents represented by electronic data such as music, moving images, and still images. In the DRM technology, a policy that describes the usage condition of a content is set for each content. A content is usable only when its policy is satisfied.
An example of content management using the DRM technology will be described. In the following description, a content protected by the DRM technology will be referred to as a protected content, and a content that is not protected by the DRM technology will be referred to as a non-protected content.
First, a content copyright holder encrypts a content and generates a license containing a decryption key to decrypt the encrypted content and a policy that sets the usage condition of the content. The encrypted content which has meta-information to acquire the license is distributed as a protected content. A consumer who has received the protected content requests the license using the meta-information attached to the protected content. The content copyright holder issues the license to only authenticated users or users who have paid for the content. Upon acquiring the license, the consumer uses the decryption key contained in the license in accordance with the policy and consumes the content.
Consumption of a content indicates processing the data of an image or a moving image and outputting it to a screen or as a printed product, or copying or editing the content. Policy evaluation to be described later indicates a process of checking whether an environment (use time or user) in using a protected content satisfies a condition described in a policy and determining whether to allow consumption of the protected content.
As another application example of the DRM technology, content distribution is restricted only on terminals and a dedicated network represented by, for example, a portable phone network. This enables to restrict use of contents on the terminals in accordance with a policy set for each content.
Normally, the DRM technology is often used to protect the copyright of a single content. Japanese Patent No. 03738020 proposes a system for protecting the copyright of a compound content including a plurality of contents.
According to this technique, a compound content includes a plurality of protected contents and has a description structure. The description structure is data which represents the relationship between the policies of the protected contents included in the compound content and aims at controlling consumption of the compound content. The description structure describes information such as “designated consumption is permitted when the policies of all protected contents are satisfied”, or “designated consumption is permitted when the policy of at least one protected content is satisfied”. When consuming a compound content, the policies of protected contents included in it are evaluated so that consumption of the compound content is controlled based on the evaluation results and the description structure.
According to the above-described conventional DRM technology, however, in consuming a compound content, it is necessary to evaluate the policies of protected contents included in it. This poses the following problems.
When repetitive consumption of the compound content is necessary, the policies of the protected contents are repeatedly evaluated, resulting in inefficiency. For example, to print the compound content or output it to a screen, the policies of the protected contents included in the compound content are evaluated one by one each time.
If it is necessary, in consuming the compound content, to consume all protected contents included in it, whether to allow use of the compound content cannot be determined until evaluation of the policies of all protected contents finishes. For this reason, a user who has requested consumption of the compound content must wait for the end of policy evaluation of all protected contents to obtain the consumption result (obtain an output to a screen).
These problems become more conspicuous as the number of protected contents included in a compound content increases.